The US Navy on Tuesday launched an operation to send a warship to within 12 nautical miles of two man-made islands in the South China Sea. Here are six things to look out for as maritime tensions escalate.

1) The South China Sea is becoming increasingly militarised. In recent years, China has built five artificial islands in the South China Sea and is constructing at least three airfields that could handle military aircraft. In response to the Chinese military presence, the USS Lassen, an Arleigh Burke class destroyer, will sail close to two of those islands. Beijing, in turn, is likely to accuse the US of militarising the region.

2) It is about control of the seas, not about who owns the islands. The US is not sending a destroyer near the man-made islands to protest China’s sovereignty claims in the South China Sea — the US insists it is neutral about the territorial disputes between China and five other countries. Instead, the US is trying to show that artificial islands do not give China control over the surrounding seas. Under international law, countries have jurisdiction over 12 nautical miles around genuine islands but not around man-made features.